# ---
# title: 822. Card Flipping Game
# id: problem822
# author: Tian Jun
# date: 2020-10-31
# difficulty: Medium
# categories: 
# link: <https://leetcode.com/problems/card-flipping-game/description/>
# hidden: true
# ---
# 
# On a table are `N` cards, with a positive integer printed on the front and
# back of each card (possibly different).
# 
# We flip any number of cards, and after we choose one card.
# 
# If the number `X` on the back of the chosen card is not on the front of any
# card, then this number X is good.
# 
# What is the smallest number that is good?  If no number is good, output `0`.
# 
# Here, `fronts[i]` and `backs[i]` represent the number on the front and back of
# card `i`.
# 
# A flip swaps the front and back numbers, so the value on the front is now on
# the back and vice versa.
# 
# **Example:**
# 
#     
#     
#     Input: fronts = [1,2,4,4,7], backs = [1,3,4,1,3]
#     Output: 2
#     Explanation: If we flip the second card, the fronts are [1,3,4,4,7] and the backs are [1,2,4,1,3].
#     We choose the second card, which has number 2 on the back, and it isn't on the front of any card, so 2 is good.
# 
# 
# 
# **Note:**
# 
#   1. `1 <= fronts.length == backs.length <= 1000`.
#   2. `1 <= fronts[i] <= 2000`.
#   3. `1 <= backs[i] <= 2000`.
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
